POLARIZATION OF THE 61ST HARMONIC FROM 1053-NM LASER-RADIATION IN NEON

We report the polarization measurement of a very high order (59th and 61st order, similar to 17 nm) harmonic. A Mo-Si multilayer mirror is u sed as a polarizer with reflectivity of 60% and polarization analyzing power close 'to unity around a wavelength of 17 nm. We observe that f or these high harmonics in Ne there is no rotation of the polarization ellipse with respect to the fundamental laser polarization, even thou gh the harmonics are in the plateau. For linear and slightly elliptica l laser polarization the harmonics still remain linearly polarized. Th ese findings are supported by a full theoretical simulation, which inc ludes spatiotemporal integration and phase matching of the emitted har monic radiation.